NUCLEAR POWER

A reactor that burns depleted fuel emerges as a potential 'game changer'

Peter Behr, E&E reporter

ClimateWire: Tuesday, February 23, 2010

Politicians and scientists speak of them hopefully as "home runs" and "game changers," the long-shot technology breakthroughs that could produce a major advance toward the nation's future climate policy goals.

After years in a status closer to science fiction than reality, the traveling wave nuclear reactor is emerging as a potential "game changer," according to a U.S. Department of Energy official. It helps that the reactor is the product of a team of top scientists backed by the deep pockets of Microsoft founder Bill Gates.

This reactor works something like a cigarette. A chain reaction is launched in one end of a closed cylinder of spent uranium fuel, creating a slow-moving "deflagration," a wave of nuclear fission reactions that keeps breeding neutrons as it makes way through the container, keeping the self-sustaining reaction going.

A "traveling wave reactor" uses depleted uranium fuel, shown in black and green. In the reaction, the uranium is bombarded by neutrons, transforming it into plutonium, which then splits or fissions. In the process, the plutonium breaks down into a spectrum of other elements, a step that some scientists say removes a nuclear proliferation hazard. Graphic courtesy of TerraPower Inc.

And it goes and goes, perhaps for 100 years, said former Bechtel Corp. physicist John Gilleland. He heads TerraPower LLC, a private research team based outside Seattle that is pursuing the traveling wave reactor design.

"We believe we've developed a new type of nuclear reactor that can represent a nearly infinite supply of low-cost energy, carbon-free energy for the world," Gilleland said in a presentation. If it can be built, a commercial version of the reactor is 15 years away or more, Gilleland acknowledged. But that could keep its development in step with the long-range policy and business investment decisions that lie ahead for the future of nuclear power fuel cycles and reactor designs.

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The venture has caught the Energy Department's eye.

"We've just been introduced to the idea," said Warren "Pete" Miller, DOE's assistant secretary for nuclear energy, who mentioned the project in his comments to last week's 2010 National Electricity Forum in Washington, D.C. "That's one innovation that could make a tremendous difference" for nuclear power.

"These are game changers if they can be deployed," said Miller, a former official at Los Alamos National Laboratory. The Massachusetts Institute of Technology's Technology Review magazine chose the traveling wave reactor last year as one of 10 emerging technologies with the highest potential impact.

Defusing a potential proliferation risk

The traveling wave reactor got another push earlier this month from Gates, at a speech about futuristic technologies that he supports through the Intellectual Ventures initiative -- a Bellevue, Wash., think tank. It is seeking "miracle" solutions on energy and health fronts. TerraPower is one of Intellectual Ventures' projects.

The reactor design could power the United States for centuries and, if smaller, modular versions can be perfected, it could also provide affordable power for poorer nations that lack large-scale nuclear power infrastructure and power grids. "With the right materials approach, this looks like it could work," Gates said.

"It's got lots of challenges ahead, but it is an example of the many hundreds and hundreds of ideas we need to move forward," he said.

The design promises singular technical and political benefits. Albert Machiels, senior technical executive at the Electric Power Research Institute in Palo Alto, Calif., said the enclosure of the traveling wave reaction defuses the threat of potential proliferation of weapons-grade nuclear materials -- a critical issue for breeder reactors.

Breeder reactors produce plutonium as part of the fuel cycle, and once chemically separated, it can be removed and used to fuel other nuclear reactors. But it may also be a target for theft by terrorists or states seeking nuclear weapons.

In the traveling wave reactor, the fuel, initially, is likely to be the vast U.S. stores of depleted uranium, which don't themselves pose a proliferation risk. Plutonium is formed in the reaction process but undergoes transmutation into other elements and is essentially consumed. Depleted uranium is a heavy, lead-like residue from making or enriching uranium fuel. Lacking the volatile isotope U-235 that is used in conventional nuclear power plant fuel and nuclear weapons, depleted uranium is currently used for conventional anti-tank ammunition and in the keels of sailboats.

Patent applications by Gilleland and his team describe two connected waves traveling through the fuel cylinder at a little less than a half-inch per month, one creating enough fast-moving neutrons to keep the chain reaction alive, and the second burning up the fuel. "Anything that minimizes the separation and isolation of plutonium is helpful," Machiels said.

An old theory being re-explored by supercomputers

Scientists began looking at the concept in the late 1950s, Machiels said. Recent developments in supercomputing have enabled the TerraPower scientists to simulate the traveling wave concept and establish its feasibility, they say.

Machiels agrees. "The modeling capability that John Gilleland's team has achieved has allowed a lot of progress. They have fantastic computing capabilities," he said. The team's supercomputer cluster has more than 1,000 times the computational strength of a desktop computer, TerraPower says.

The team draws on support from MIT, DOE's Argonne National Laboratory and other scientific centers, and future testing will require more DOE support. But at this point, the project is a private research venture.

It recalls the famous Tuxedo Park laboratory established by the millionaire investor and amateur scientist Alfred Lee Loomis at his mansion outside New York City in 1926. Its scientists went on to provide critical research in the development of radar and the atomic bomb in World War II.

"This is a type of work that requires a deep, deep pocket," said Machiels. "The fact that this is being funded now by a private firm is good, but very unusual." TerraPower is backed by Nathan Myhrvold, Microsoft's former chief technology officer, who now is CEO of Intellectual Ventures.

Creating pilot demonstrations to verify the theory and computer simulations of the fuel cycle is one of the technology's remaining challenges. Another is finding alloys for the reactor cylinders that can withstand the heavy damage caused by neutron impacts.

Duncan Williams, writing last fall on the Nuclear Street blog site, noted that no one has made a deflagration wave work yet -- it has only been demonstrated with simulation software. "So it seems that this technology has many years to go before it becomes a physical reality," he said.

"We cannot expect it is going to be delivered soon," Machiels agreed.

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